The respiratory distress syndrome of infancy (RDS) is felt to be secondary to a lack of pulmonary surfactants. A pilot study suggested the efficacy of replacing at least two of these surfactants (by nebulization of an aqueous solution of phospholipid vesicles (90% dipalmitoyl phosphatidyl choline (DPPC) and 10% dipalmitoyl phophatidyl glycerol (DPPG)) to infants requiring ventilatory assistance for RDS. The objectives of the current project were twofold: 1) to carry out a more extensive controlled trial in humans using DPPC/DPPG and a placebo to establish the efficacy of this treatment, and 2) to investigate in an animal model, the relative effects of varying the percentage of DPPG, as well as the effects of addition of other components of the surfactant complex (phosphatidyl serine, phophatidyl inositol, lysolecithin, cholesterol and albumin) to DPPC. To date, the major emphasis has been with the animal model, the preterm lamb with RDS. Preterm lambs at about 132 days gestation are delivered by Ceasarian section, resuscitated, incubated and placed on respirators. The trachea is ligated, and esophageal balloon is inserted, an umbilical arterial catheter is placed and baseline arterial blood gases, as well as compliance studies, are obtained. If it is established that the lamb has RDS, nebulization of a mixture of two of the above mentioned substances is begun. The mixture is supplied as an unknown. It is sonicated to form vesicles, administered in a dose of approximately 3mg/kg and is nebulized qlhr x6. Arterial blood gases and compliance studies are obtained at least every hour. At the termination of the experiment, the lamb is sacrified and post mortem compliance studies are performed with closed an open thorax. The plan is to administer various combinations of the above mentioned substances, at varying percentages, to lambs is duplicate or triplicate. The most promising combinations will be pursued in depth.